The Federal Communications Commission (FCC) is an independent agency of the United States government that is charged with regulating all non-federal government use of the radio spectrum (including radio and TV broadcasting), and all interstate telecommunications (wire, satellite and cable) as well as all international communications that originate or terminate in the United States. In 2010, the FCC finalized rules approving the unlicensed signal operation in the unused TV channels (i.e., white space). The new rules allow wireless technologies to use the TV white space as long as the technology and any resulting signal transmissions do not interfere with the existing primary users. For example, cognitive devices, such as white space devices, are allowed to use TV frequency bands if they do not cause harmful interference to TV receivers. Thus, cognitive radio demands a technology that can continuously sense the environment, dynamically identify unused spectral segments, and then operate in these white spaces without causing harmful interference to the incumbent users. Cognitive radio is a paradigm for wireless communication in which either a network or a wireless node changes its transmission or reception parameters to communicate efficiently avoiding interference with licensed or unlicensed users.
There are three types of primary signals: digital TV, which follows the ATSC format in North America; analog TV, which follows the NTSC format; and wireless microphones, which are narrowband (less than 200 kHz) signals with tunable operating frequency and generally use analog frequency modulation (FM). Other applicable signals include any applications that are entitled by regulations to use a specified portion of the spectrum. For purposes of this disclosure, the various devices that utilize such technologies to access this TV white space will be referred to as “white space devices,” “unlicensed devices,” “white space sensing devices,” or the like.
White space devices with spectrum sensing capability generally operate in a cognitive manner in which the devices first scan to detect TV band signals from licensed primary users. The white space devices will then select unused channels in order to avoid interference with the licensed signals. Therefore, these white space devices generally share two common functions: (1) sensing for incumbent signals; and (2) selecting appropriate channels for interference avoidance.
The unprecedented radio agility envisioned, calls for fast and accurate spectrum sensing over a wide bandwidth, which challenges traditional spectral estimation methods typically operating at or above Nyquist rates. The radio front-end can employ a bank of tunable narrowband bandpass filters to search one narrow frequency band at a time. In each narrowband, existing spectrum sensing techniques perform either energy detection or feature detection. A major implementation challenge lies in the very high sampling rates of conventional spectral estimation methods, which have to operate at or above the Nyquist rate. Meanwhile, due to the timing employed for rapid sensing, only a limited number of measurements can be acquired from the received signal, which may not provide sufficient statistics when traditional linear signal reconstruction methods are employed.
Accordingly, it would be desirable to perform spectrum sensing of narrowband features in a wireless channel with less complexity in order to increase sensing performance.